After 20 games Stockfish leads 3-2 with 15 draws. Stockfish wins the first decisive game pair of the match. There was another game pair with two white wins. So far neither engine seems to be stronger, still early in the match.
Games 11-12 started with a rare line in the Dutch defense where white has a significant eval advantage. In game 11 Leela gave a knight for 3 pawns, leaving the center and king side almost clear of black pawns. After exchanging queens the black king was forced to move, blocking Stockfish's queen side pieces.
Evals continued to increase gradually, the black king stayed in the center surrounded by pieces. Leela opened a file on the queen side and shifted its rooks there, while slowly pushing its central pawns forward. The 4 connected pawns started to look intimidating.
Stockfish gave a rook for a bishop and managed to remove two white pawns. Leela pinned the black knight on the back rank and the black king could not move. Leela had a protected passer on the 6th rank facing the king and Stockfish had to focus its available pieces on defense. The engines exchanged bishops and only RR vs RBN remained.
Leela pushed the b pawn forward and the black defense crumbled, the d pawn became a connected passer before the game ended.
There were only a few exchanges after the start of game 12. Leela pushed pawns forward and gave a rook for a knight, then gave a knight for two pawns. Leela was determined to attack the exposed white king even at the price of a piece, however Stockfish's eval increased over 2.5.
Stockfish gave a bishop back, it was almost trapped in any case. The white queen came forward and Stockfish started attacking from the king side. With a white rook on the open f file the black king was in danger. Leela's advanced pawns looked dangerous but there was no time to move them while Stockfish threatened mate.
Leela managed to get one pawn to the 2nd rank but had to give up both central pawns to save its king. Stockfish had a winning advantage in a QR vs QB position and a pawn up. Two white wins in this game pair, the score is still tied.
The engines castled in opposite directions and opened a file in the center in game 13. Leela placed a pawn on f6 with the white queen on the king side while Stockfish pushed pawns on the queen side facing the white king. Leela stopped the black pawns, went a pawn up and created a queen side passer. Stockfish reduced to a QRB vs QRN position and its eval came down. Leela concentrated on its passer, it lost two pawns but after exchanging queens the passer reached the 7th rank. Stockfish lost the knight for the passer, the remaining black pawns were good for a draw against the white bishop. In game 14 Stockfish's eval was around 1 for a short while, both engines castled short and the center was open. Evals came down as the engines exchanged pieces and pawns, the game reached a double rook ending on move 28. The engines continued to play with exchanges and pawn moves, the game was adjudicated on move 51.
Games 15-16 started with a 20-ply book in the Gruenfeld defense, Smyslov variation. There were many early exchanges in game 15 and only RBN vs RBN remained on move 24. The engines reduced to a drawn rook ending, Leela wouldn't lower its eval and the game was adjudicated only on move 77. In game 16 the engines kept the queens on the board a little longer, the game reached a RBN vs RBN position on move 32. Stockfish was a pawn up, it gave the pawn back to create a passer on the queen side. Leela gave a rook for a bishop to stop the passer, all the remaining pawns were on the king side and Stockfish could not improve its position despite the material advantage. The engines shuffled until Stockfish lowered its eval for the draw rule on move 89.
Games 17-18 started in a Sicilian Taimanov variation that was played in a Karpov-Kasparov game. In game 17 Leela castled long and Stockfish kept its king in the center. The engines exchanged most minor pieces, Leela tried to force its way through the king side and Stockfish's eval went over 1 after the h file was opened. A series of exchanges reduced to a B vs N ending and Stockfish's eval dropped to 0. Leela was a pawn up, all pawns were passers and the black pawns were a little more advanced than the white ones. Both engines were not strong enough to push their own pawns while blocking their opponent's pawns, eventually they started to shuffle. Leela's eval came slowly down and the game ended on move 101.
Game 18 started similarly, Stockfish castled long and Leela kept its king in the center. There were fewer exchanges, Leela tried to threaten the queen side through an open file. Stockfish's eval was around 1.5, Leela gave a pawn and opened another file on the queen side to add pressure, Stockfish created a passer on the king side. Leela's eval was under 1 while Stockfish concentrated forces in the center, then suddenly Stockfish's eval jumped over 6 as it broke through the center with a sacrifice of a rook and a knight for a bishop and two pawns.
Leela saw the danger a move too late. The immediate problems were the white h pawn and the exposed black king. While Leela tried to defend Stockfish captured 3 more pawns and pushed both the d and the h pawns to the 6th rank.
Stockfish exchanged the last black pawn and a pair of rooks. It gave up the passer on the king side, instead pushed a second passer towards the black king. After the bishops were exchanged Leela could not prevent a pawn promotion. First game pair win of the match goes to Stockfish.
Stockfish's eval dropped to 0 early in game 19, Leela's eval was also low. Leela castled long after all the knights were exchanged, Stockfish gave a pawn and opened the queen side. For a while Leela had an advanced passer, it was gone in a series of exchanges and only RRB vs RRB remained on move 29. The exchanges continued until each engine had only one pawn left and the game was adjudicated. Evals were low in game 20 as well. Stockfish castled long and this time the knights stayed on the board. After a while Leela pushed through the king side, creating a passer and capturing two pawns. Stockfish reacted with a rook sacrifice and a mate threat. Leela was forced to give its queen for a rook, Stockfish could have forced a perpetual check but it stopped repeating. However the game was adjudicated as both engines agreed the QN vs RRB position was a draw.
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